<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Bootstrap-下拉菜单</title>
    <link href="bootstrap-3.3.7-dist/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<div class="dropdown">
    <button type="button" class="btn dropdown-toggle" id="dropdownMenu1" data-toggle="dropdown">
        主题<span class="caret"></span>
    </button>

    <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
        <li role="presentation" class="dropdown-header">下拉菜单</li>
        <li role="presentation">
            <a role="menuitem"  href="#">Java</a>
        </li>
        <li role="presentation">
            <a role="menuitem"  href="#">数据挖掘</a>
        </li>
        <li role="presentation">
            <a role="menuitem" href="#">数据通信/网络</a>
        </li>
        <li role="presentation" class="divider"></li>
        <li role="presentation">
            <a role="menuitem" href="#">分离的链接</a>
        </li>
    </ul>
</div>

<div class="dropdown">
    <button type="button" class="btn dropdown" data-toggle="dropdown" id="dropdownMenu2"><span class="caret"></span>主题</button>
    <ul class="dropdown-menu" aria-labelledby="dropdownMenu2">
        <li class="dropdown-header">选择数字</li>
        <li>111</li>
        <li>2222</li>
        <li class="divider"></li>
        <li>333</li>
    </ul>
</div>
<script src="jquery-3.2.1.js"></script>
<script src="bootstrap-3.3.7-dist/js/bootstrap.min.js"></script>
</body>
</html>